In a VSCF power generating system, a generator is supplied variable-speed motive power by a prime mover, such as an aircraft engine, and develops variable-frequency AC power at an output thereof. The variable-frequency power is rectified and provided over a DC link conductor to a controllable inverter. The inverter is operated to produce constant-frequency AC power, which is then supplied over a load bus to one or more loads. A control unit controls the excitation of the generator or the inverter or both in order to regulate the output of the generating system. Such a control is disclosed in Rozman, et al., U.S. Pat. No. 4,937,723. A control of this type must be used in conjunction with, for example, an AC voltage detector to sense the output voltage of the VSCF system at a point of regulation (POR) in order to regulate the output voltage. The VSCF system requires the use of an AC voltage detector having fast response characteristics for improved transient performance. Currently the AC voltage detector is implemented with a rectifier and a filter. This filter slows down the transient response of the detector resulting in poor system performance.
Other patents disclosing controls for VSCF power supply systems wherein generator excitation is controlled in accordance with one or more sensed parameters include Hucker, U.S. Pat. No. 4,442,396 and Glennon, U.S. Pat. No. 4,622,629.
Rozman, et al., U.S. Pat. No. 5,047,699 discloses a VSCF system which is operable in generating and starting modes. When the VSCF system is operating in a starting mode, input power is provided to a rectifier and inverter of the VSCF system, which in turn operate a brushless generator as a motor to provide motive starting power. A motor current estimator is operative during the starting mode of operation to estimate the current flowing in the generator armature windings. The current estimator is responsive to an input power signal representing the input power provided by an external source during operation in the starting mode, a rotor position signal and a commutation angle command signal.